Chapter 18: Designing for Different Needs

As we discussed in Part I, personas and scenarios provide designers with strong guidance for establishing and designing for the basic goals, behavior patterns, and needs of users. However, even though we optimize our design for personas, individual needs shift over time, and there are variations in behavior among individuals and subgroups of users that ought to be addressed by a truly robust interface. This chapter explores various concepts and design ideas for coping with the different needs of different users within the larger context of a design framework.

Command Vectors and Working Sets

Two concepts are particularly useful in sorting out the needs of users with different levels of experience: command vectors and working sets. Command vectors are distinct techniques for allowing users to issue instructions to the program. Direct manipulation handles, drop-down and pop-up menus, toolbar controls, and keyboard accelerators are all examples of command vectors.

Good user interfaces provide multiple command vectors, where key functions in the program are provided in the form of menu commands, toolbar commands, keyboard accelerators, and direct manipulation controls, each with the parallel capability to invoke a particular command. This redundancy enables users of different skill sets and preferences to command the program according to their desires and abilities.

Immediate and pedagogic vectors

Direct manipulation controls, like push-buttons and toolbar controls, are immediate vectors. There is no delay between clicking a button and seeing the results of the function. Direct manipulation also has an immediate effect on the information without any intermediary. Neither menus nor dialog boxes have this immediate property. Each one requires an intermediate step, sometimes more than one.

Some command vectors offer more support to new users. Typically, menus and dialog boxes offer the most, which is why we have named them pedagogic vectors. Beginners avail themselves of the pedagogy of menus as they get oriented in a new program, but perpetual intermediates often want to leave them behind to find slimmer, more immediate vectors.

Working sets and personas

Because each user unconsciously memorizes commands that are used frequently, perpetual intermediates memorize a moderate subset of commands and features, a working set. The commands that comprise any user's working set are unique to that individual, although it will likely overlap significantly with other users who exhibit similar use patterns when working with the application. In Excel, for example, almost every user will enter formulas and labels, specify fonts, and print; but Sally's working set might include goal-seeking, whereas Elliot's working set includes linked spreadsheets.

Although, strictly speaking, there is no such thing as a standard working set that will cover the needs of all users, research and modeling of users and their use patterns can yield a smaller subset of functions which designers can be reasonably confident are accessed frequently by most users. This minimal working set can be determined via goal-directed design methods: by using scenarios to discover the functional needs of your personas. These needs translate directly to the contents of the minimal working set.

The commands in any person's working set are those used frequently. The user wants those commands to be especially quick and easy to invoke. This means that the designer must, at least, provide immediate command vectors for the minimal working set of the most likely users of the application.

Although a program's minimal working set is almost certainly part of each user's full working set, his individual preferences and job requirements will dictate which additional features are included. Even custom software written for corporate operations can offer a range of features from which each user can pick and choose. This means that the designer must, while providing immediate access to the minimal working set, also provide means for promoting other commands to immediate vectors. Similarly, immediate commands also require more pedagogic vectors to enable beginners to learn the interface. This implies that most functions in the interface should have multiple command vectors.

There is an exception to the rule of multiple vectors: Dangerous commands (like Erase All, Clear Undo, Abandon Changes, and so on) should not have easy, parallel command vectors. Instead, they need to be protected within menus and dialog boxes (in keeping with the axiom: Hide the ejector seat levers (Chapter 9).